Flat panel displays (FPD) such as liquid crystal displays and plasma displays are currently used for many of various electronic devices such as displays for display devices of computers or television image receiving devices and display parts of portable telephones. In a process for manufacturing such an FPD, it is needless to say that waste solutions are produced and it is necessary to treat these waste solutions. This is the same to not only to liquid crystal manufacturing factories where such an FPD is treated but also to semiconductor manufacturing factories and plating factories. Then, there is an etching waste solution containing indium and ferric chloride as one of these waste solutions generated in the processes of manufacturing such an FPD.
Generally, industrial waste solutions sometimes contain various metals. In and the like are contained in waste solutions from liquid crystal manufacturing factories for manufacturing the FPD, copper (Cu), gallium (Ga) and the like are contained in waster solutions from semiconductor manufacturing factories, and nickel (Ni), Cu, zinc (Zn) and the like are contained in waste solutions from plating factories. An attempt is made to recover these metals as valuables. If these metals can be recovered in the form of metal simple substances or alloys, these metals can be, for example, reused.
As conventional technologies for treating waste solutions to recover heavy metals, the coagulation sedimentation treatment, coprecipitation treatment, or the like using chemicals is usually adopted. When the concentration of metals is low, these metals are removed by using an adsorbent. For example, as technologies utilizing the coagulation sedimentation treatment using chemicals, there is the invention described in the following Patent Document 1.
However, when the coagulation sedimentation treatment as mentioned above is applied to the etching waste solution containing indium and ferric chloride, indium can be recovered in the form of indium hydroxide. However, ferric chloride is also precipitated as a hydroxide, resulting in the problem that the amount of sludges of hydroxides generated is increased as a whole. Also, almost all sludges are put into iron-containing sludges, resulting in the problem that these metals are not recovered as valuables.
The present inventors and the like have researched prior art concerning a method of removing or recovering indium from an etching waste solution containing indium and ferric chloride, and as a result, have found that the patent application described in the following Patent Document 2 only exists. Specifically, the invention described in this Patent Document 2 relates to a method for removing or recovering indium, characterized in that iron and a nickel compound are added to an etching waste solution containing indium and ferric chloride as described in claim 1 thereof.
As for specific recovering means, there are the descriptions, in the paragraph [0022] of the specification of Patent Document 2, reading as follows “A nickel compound is added, then iron is added to the waste solution, and the mixture is heated with stirring to precipitate nickel and also indium. From this fact, indium can be removed from the waste solution. In other words, indium can be recovered from the precipitate . . . ”. There are also the descriptions in the paragraph [0023], reading as follows “The mixture consisting of indium and nickel precipitated by adding iron to the etching waste solution containing indium and ferric chloride is stuck to iron and can be therefore simply separated from the solution as a precipitate. Examples of a method of separating the precipitate may include the gravity type sedimentation, filtration and methods utilizing centrifugation such as a method using a cyclone.”.
Inferring from these descriptions, a nickel precipitation reaction is caused by the addition of nickel ions and this nickel precipitation reaction is accompanied by an indium precipitation reaction in the method of Patent Document 2. Therefore, the recovered indium alloy is much reduced in indium concentration and is recovered in the form of an alloy primarily containing nickel. In this point, Patent Document 2 does not refer to a method of separating the recovered indium alloy. Therefore, though the method as described in Patent Document 2 may be used as technologies for removing indium from a waste solution, the method is unnecessarily regarded as technologies that can be effectively utilized as technologies for recovering only indium as a valuable.    Patent Document 1: JP-A 2005-342694    Patent Document 2: JP-A 2004-75463